Quick Tip: Diff Two Directories and Get a Clean Summary with `diff -qr` (No GUI Needed)

Quick Tip

Someone asks "what's different between these two folders?" and people reach for a GUI tool or start writing a Python script. diff already does it:

diff -rq dirA/ dirB/

Output is exactly what you want — nothing else:

Only in dirA/: config.local.yml
Files dirA/app.py and dirB/app.py differ
Only in dirB/logs: error.log

Three lines tell you: one file only exists locally, app.py has drifted, and there's a stray log on the other side.

The flags that matter:

Flag	What it does
`-r`	Recurse into subdirectories
`-q`	Report only whether files differ, not the diff itself
`--brief`	Same as `-q` (GNU)
`-x PATTERN`	Exclude files (e.g. `-x '*.pyc' -x '__pycache__'`)

Real use case from last week — verifying a deploy actually copied everything:

diff -rq --exclude='.git' --exclude='node_modules' \
  ./build/ /var/www/app/
# no output = byte-identical trees = deploy was clean

Want the actual differences for just the files that drifted? Pipe it:

diff -rq dirA/ dirB/ | grep '^Files' | cut -d' ' -f2 | \
  xargs -I{} sh -c 'echo "=== {} ==="; diff {} $(echo {} | sed s/dirA/dirB/)'

Works on every Linux/macOS box you'll ever SSH into. Zero installs, zero network, zero excuses.